Optical fiber connectors and splicing devices are an important part of substantially any optical fiber communication systems. For instance, connectors or splicing devices may be used to join segments of fiber into longer lengths or to connect fiber to active devices such as radiation sources, detectors, or repeaters, or to passive devices such as switches or attenuators. Considering that a core of multimode optical fiber is 50 microns in diameter and that of single mode fiber is 8 microns, the connection or splicing is no small task.
An optical fiber connector is disclosed in U.S. Pat. No. 4,850,670 which issued on Jul. 25, 1989 in the names of T. D. Mathis and C. M. Miller, and which is assigned to the assignee of the instant application. The above patent discloses an optical fiber connector that utilizes two drawn glass capillary tubes that serve to hold two fiber end portions and allow alignment of the ends by means of a simple alignment sleeve. These capillary tubes commonly are referred to also as ferrules. The disclosed connector serves completely satisfactorily with multimode fibers, for which, due to their relatively large core diameter, alignment to within a few microns is generally acceptable. The connector also has been found frequently to give satisfactory results with single-mode fibers. However, it is not always easy to achieve very low-loss connections, that is, connections having a loss of the order of 0.1 dB.
The making of single-mode connections in the prior art typically has involved the active alignment of the fiber ends. Prior art methods comprise translating one fiber end relative to the other, typically by means of a precision stage, until maximum energy coupling across a gap therebetween is observed, for example, by means of a remote detector. As will be appreciated, such a procedure is both difficult to carry out in the field and requires highly skilled personnel.
Drawn glass or other ferrule-type fiber connectors and splicing devices generally offer low cost, simplicity, relatively low-loss single-mode connections, environmental stability, and versatility. Because of these advantages, a connector or splicing device that includes a capillary tube drawn from glass or other material would be of considerable importance.
A somewhat recent entry into the field of optical fiber splicing devices is one which commonly is referred to as the rotary splice. The splicing device is disclosed in U.S. Pat. No. 4,545,644 which issued on Oct. 8, 1985 in the names of G. F. DeVeau, Jr. and C. M. Miller. The rotary splice device comprises two capillary tubes, and preferably three alignment rods consisting preferably of the same material as the capillary tubes in fixed radial and axial relationship to each other. The alignment rods are of generally cylindrical shape, with typically two of them including a flat that is to extend from one end over a substantial fraction of the length of the rod. It is the presence of these, suitably placed, flats which allows alignment of the fiber ends to within exceedingly close tolerances.
Notwithstanding the availability of the above-described splicing device, the search for a reliable optical fiber splicing device has continued. Sought after is a splicing device that is relatively simply and easily installed in the field, that is rugged, and that has acceptable temperature cyclability. Also, the sought-after splicing device should be one which provides a connection having a loss which is sufficiently low to obviate the need for expensive precision alignment apparatus. Further, it has long been desired to provide a relatively low cost optical fiber splicing device for general usage. Also, the splices which are achieved with many of the prior art devices require the use of adhesive materials or gels which require curing. It would be most desirable to have available a mechanical splice which does not require the use of materials to be cured.
A more recently developed optical fiber splicing device is one which is described as cleave, sleeve and leave. In it, end portions of optical fibers are caused to be disposed in a capillary tube with center portions exposed. A flexible metallic member in the center of the capillary tube is folded over the spliced end portions to retain the spliced portions in engagement with each other.
There is another feature which is desired in the sought-after splicing device. Considering the dimensions of the transmission media to be spliced, it would be highly desirable to be able to inspect the spliced ends of the optical fibers without the need for expensive apparatus. A splicing device which includes this feature does not appear to be available in the prior art.
What is desired and seemingly what is not available in the prior art is a relatively low cost, mechanical optical fiber splicing device which does not involve curable materials and which allows inspection of the spliced ends of the optical fibers. The sought-after splicing device should be one which is simplistic in structure yet one which provides a reliable relatively low loss and relatively low return loss splice connection.